Experimental comparison of caudal wedge ostectomy to cranial wedge ostectomy for surgical treatment of overriding/impinging spinous processes in horses.

Abstract

Background: Caudal wedge ostectomy has not been investigated for overriding or impinging spinous processes (SPs).

Objectives: To establish the feasibility of caudal wedge ostectomy and compare measures of surgical trauma and error between hypothetical caudal and cranial wedge ostectomies on SPs of different inclinations.

Study design: Experimental, method comparison study.

Methods: Computed tomography and caudal wedge ostectomy surgery were performed on four cadavers. Observations, technical difficulties, and surgical errors were recorded. Radiographs from 67 horses with overriding/impinging SPs were reviewed. Hypothetical 'ideal' caudal and cranial wedge ostectomies, and 'error' ostectomies 12° from ideal, were drawn at sites of impingement. Ostectomy area/SP width, ostectomy length/SP width, absolute difference of exit angles (angle ostectomy exits the SP) from 90°, and number of error ostectomies failing to exit the SP (never-ending-cuts [NEC]) were calculated. Continuous variables were compared between techniques in caudally and cranially inclined SP groups using Wilcoxon signed-rank tests. Proportions of NEC were compared using McNemar's tests.

Results: No surgical errors were recorded with caudal wedge ostectomy. Median ostectomy area/SP width was lower for caudal versus cranial wedge ostectomy in caudally (14.32, interquartile-range [IQR] 9.72-20.34 vs. 25.57, IQR 17.74-33.06; p < 0.001) and cranially inclined SP groups (11.78, IQR 7.98-17.19 vs. 19.62, IQR 13.65-28.68; p < 0.001). Median difference in exit angles from 90° was smaller for caudal versus cranial wedge ostectomies in caudally (34.77°, IQR 26.85°-45.91° vs. 67.54°, IQR 58.13°-74.55°; p < 0.001) and cranially inclined SP groups (49.14°, IQR 35.61°-59.33° vs. 62.84°, IQR 55.34°-70.61°; p < 0.001). The proportion of NEC was lower for caudal versus cranial wedge ostectomy in caudally (37.6%, 95% confidence interval [CI] 29.4%-45.8%; n = 50/133 vs. 96.2%, 95% CI 93.0%-99.5%; n = 128/133; p < 0.001), but not in cranially inclined SP groups (76.8%, 95% CI 70.9%-82.7%; n = 152/198 vs. 84.3%, 95% CI 79.3%-89.4%, n = 167/198; p = 0.06).

Main limitations: Potential bias drawing 'ideal' ostectomy.

Conclusions: Experimentally, caudal wedge ostectomy was feasible, removed less bone, and resulted in fewer NEC in caudally inclined SPs. Further investigation of the technique is warranted.